1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device that receives and outputs low amplitude differential signals.
2. Description of Related Art
Testing of an integrated circuit (hereinafter, termed “IC”) has been conducted heretofore for an improvement in the reliability and quality thereof. In a case where an IC is to be tested, a signal for switching the IC from a normal operation mode to a test mode is inputted to the IC from the outside thereof.
As a method of switching an IC from a normal operation mode to a test mode as described above, the following technique is described in Patent Documents 1 and 2. In the technique described in Patent Document 1, a voltage higher than the power supply voltage is inputted to a normally-used input/output terminal, as shown in FIG. 15. The IC is set to the test mode upon detecting a voltage higher than the power supply voltage. On the other hand, in the technique described in Patent Document 2, a terminal used for setting a test mode is additionally provided, as shown in FIG. 16. In the case of Patent Document 2, the IC is set to the test mode when a signal having a predetermined voltage is inputted to this terminal from the outside of the IC.
In the technique described in Patent Document 1, however, since the signal to be inputted has a voltage higher than the power supply voltage, there is a possibility that a voltage greater than the element breakdown voltage is inputted. For this reason, the chip size becomes larger in order to allow the element breakdown voltage to have enough margin in some cases. Moreover, in the technique described in Patent Document 2, since the terminal used for the test mode is provided, that is, since a terminal unnecessary for the normal operation is formed, the chip size eventually becomes larger.
[Patent Document 1] Japanese Patent Application Laid-open Publication No. 2000-338145
[Patent Document 2] Japanese Patent Application Laid-open Publication No. 2002-123501
As described above, in order to make the semiconductor device capable of receiving a signal for setting it to a test mode or the like, the chip size thereof becomes larger in some cases.